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The Hawks held off the approaches of rival teams to snare the 23-year-old former Cavs small forward.
Adel, who was born in South Sudan but raised in Melbourne, returns to Australia after most recently playing for the Long Island Nets of the G League.
Newly acquired coach, Brian Goorjian played a major part of the Hawks pitch to Adel, who believes the six-time NBL champion coach is the man to help him find his way back onto an NBA roster.
"It was a big factor," Adel said.
"I'm trying to develop my game and I want to grow every year, and I think the resume that he has speaks for itself.
"I want to be in that type of environment where I can work every day and be challenged by the coach, and a coach that is willing to put himself out there for the betterment of the players."
The addition of Adel is the fifth signing for the Hawks as they attempt to rebuild their roster from scratch.
He joins previous signings Emmett Naar, Deng Deng, Dan Grida and Sam Froling in the club’s recruitment drive.
Goorjian said Adel was a crucial signing and one which would help set a foundation in the club’s rebuild.
"Deng is an NBA-level talent and at just 23-years-old, he holds aspirations to make the NBA again," Goorjian said.
"The fact he has put his trust and faith in the Hawks' program to help him on that journey is a great endorsement of the organisation and its direction under new ownership.
"On the court, Deng is going to help tremendously as we construct a roster that will help establish a winning culture for the club."